The present application for patent is entitled to the benefit of an earlier filing date in a foreign country under 35 U S C. 119, based on Brazilian application Serial No. P19203110, Aug. 12, 1992, which is hereby incorporated by reference.
This invention relates to the preparation of modified aluminas and their use in cracking catalysts. More particularly, the invention relates to the preparation of modified aluminas using low-molecular weight organic acids and their use in fluidizable cracking catalysts for cracking heavy hydrocarbon feedstocks, especially those containing metals.
Heavy hydrocarbon feedstocks generally are contaminated by various materials, including metals. More particularly at issue here are nickel and vanadium contaminations, since during the catalytic cracking of such feedstocks they w111 be captured by the cracking catalyst and poison it. Such poisoning causes reduced catalyst activity and a decrease of the selectivity to valuable cracking products such as gasoline, together with the production of additional quantities of objectionable products such as hydrogen, gas, and coke. Research has shown that the presence of nickel leads to increased hydrogen and coke production, as indeed does vanadium to some extent, although the principal effect of vanadium is that it attacks the catalyst""s zeolite structure, as a result of which there is deterioration of the catalyst activity. The prior art has provides a wide range of proposals for solving this problem of catalytically cracking heavy, metals-containing feedstocks.
Thus, U.S. Pat. No. 4,283,309 proposes a cracking catalyst especially suited for use in cracking heavy, metals-containing feedstocks which is composed of a crystalline aluminosilicate, an inorganic oxide gel, and a porous inorganic oxide. The surface area of this porous inorganic oxide is greater than 200 mg and at least 0.2 ml/g of the pore volume should be in pores ranging in diameter from 90 to 200 xc3x85; these parameter values were determined on the material after its calcination at 538xc2x0 C. for 6 hours and independent of the other catalyst components. Such materials may be made up of alumina, titania, silica, zirconia, magnesia, and combinations thereof. In addition, it is stated that the final catalyst, after steam deactivation, has such a pore size distribution that at least 0.4 ml/g of the pore volume is in pores of greater than 90 A in diameter.
An alternative proposal is put forward in European Patent Application No. 0 176 150. This document recommends the use of a physical admixture of zeolite-containing cracking catalyst particles and alumina particles, stating that the metal contaminants are preferentially captured by the alumina particles and, in consequence, hardly if at all by the zeolite-containing particles. GB Patent No. 2,116,062 likewise recommends the use of alumina particles separately from the zeolite-containing cracking catalyst; these alumina particles have a specific surface area of from 30 to 1000 m2/g and a pore volume of from 0.05 to 2.5 ml/g.
Despite these types of proposals, there continues to be a need for novel catalysts suitable for the catalytic cracking of heavy, metal-containing feedstocks. It has now been found that a particularly suitable catalyst may be obtained when the additive employed is an alumina modified using a low-molecular weight organic acid. The invention relates to a process for preparing said additive, the additive itself, to zeolite-containing cracking catalysts containing said additive, and to the use of these catalysts in cracking heavy feedstocks. It has been found that the catalysts according to the invention possess excellent metal resistance and also effect good bottoms conversion.
According to the invention, the modified alumina is prepared by means of a process involving contacting a hydrated alumina at a temperature in the range of 25xc2x0 to 110xc2x0 C. for a period of 1 to 100 hours with an aqueous solution of a monocarboxylic acid having from 1 to about 3 carbon atoms, preferably selected from the group of formic acid, acetic acid, and propionic acid, the end pH being about 4 or less, and isolating the solid reaction product.
The resulting products are modified aluminas comprising hydrated aluminas and at least one aluminum salt of a monocarboxylic acid having from 1 to about 3 carbon atoms, preferably selected from formic, acetic and propionic acids. These aluminas have improved porosities, as discussed below. The calcined versions contain less water of hydration in the hydrated alumina portions.
Further in accordance with the invention, fluidizable cracking catalysts are prepared which comprise a matrix (preferably comprising an inorganic or metal oxide), from about 5 to about 50 weight percent of a crystalline, zeolitic aluminosilicate and from about 2 to about 80 weight percent of the modified alumina described above.
The invention also encompasses processes of catalytically cracking metals-containing hydrocarbon feedstocks which comprise steps of contacting such feedstocks with a catalyst prepared in accordance with the invention.